Hans Wennborg has announced LLVM 4.0 RC3. "4.0.0-rc3 was just tagged from the branch at r296762. This is a release candidate in the real sense: if no major issues show up with this one, it is the version that will be released."
LLVM/Clang 4.0 changes are outlined in our LLVM 4 feature overview. Look for the official release to come in the days ahead.